1. Field of the Invention
The present invention relates to a coinjection nozzle having thermally separated melt channels, typically used in the hot runner system of an injection molding machine.
2. Description of Related Art
Coinjection molding is typically used to mold multi-layered plastic packaging articles having a laminated wall structure. Each layer is typically passed through a different annular or circular passageway in a single nozzle structure and each layer is partially, sequentially, injected through the same mold gate. In such multi-material molding applications, melts (often plastic resins) with different operating temperature requirements flow through a coinjection nozzle which has only a single or uniform temperature control, typically provided by a nozzle heater which heats the entire nozzle. This may lead to inaccurate or improperly molded parts because each of the various resins may not be at its optimum operating temperature during a particular molding operation. Also, the molding cycle time may have to be lengthened to allow for the different temperature requirements of the different melts. Further, the coinjection nozzle may have to be made larger to provide some minimal thermal separation between the different melt channels.
U.S. Pat. No. 4,717,324 to Schad discloses a coinjection hot runner system including a valve gated nozzle design having two melt channels, each located in different components forming the nozzle assembly. The patent discloses one method to maintain the two resins at different operating temperatures during their passage through the nozzle assembly from the nozzle's interface with the hot runner manifold to the gate to the mold cavity. In the '324 patent, the nozzle assembly comprises concentric components separated from each other by an air gap, for most of the nozzle's length. At the nozzle tip, however, an outer nozzle housing component locates and seals against the mold gate insert and consequently has poor thermal insulation at that interface. This allows substantial heat loss from the nozzle heater, and causes poor thermal management at the nozzle tip/gate interface.
U.S. Pat. No. 5,030,077 to Orimoto discloses a coinjection hot runner nozzle having concentric melt channels for the various resins, with the central channel having a movable tip that blocks a surrounding channel when resin flows through the central channel. Such a movable tip increase manufacturing and maintenance costs. There is no disclosure about how to thermally insulate the nozzle assembly from the mold cavity or its environs. Moreover, access to service the nozzle tip is complicated.
U.S. Pat. No. 5,897,822 to van Manen discloses a valve gated coinjection hot runner nozzle having a concentric melt channel for a single resin. The thermal insulation at the gate area is poor and the nozzle must be completely dismantled to service the tip and gate area.
U.S. Pat. No. 5,935,615 to Gellert discloses a coinjection hot runner nozzle having a concentric melt channel for one resin. Access to service the melt channels and tip is difficult.
U.S. Pat. No. 6,261,075 to Lee discloses a valve gated coinjection hot runner nozzle having separately drilled channels for two resins, on either side of the valve stem. Access to service the melt channels and tip is difficult. See also:
U.S. patent application Ser. No. 10/879,576 entitled INJECTION MOLDING MACHINE SHOOTING POT WITH INTEGRAL CHECK VALVE;
U.S. patent application Ser. No. 10/879,581 entitled INJECTION MOLDING MACHINE SPIGOTTED SHOOTING POT PISTON
U.S. patent application Ser. No. 10/879,621 entitled APPARATUS AND METHOD FOR SEALING INJECTION UNIT AND SPRUE;
U.S. patent application Ser. No. 10/879,575 entitled APPARATUS AND METHOD FOR ACTUATION OF INJECTION MOLDING SHOOTING POTS;
U.S. patent application Ser. No. 10/879,582 entitled CONTROL SYSTEM FOR A DYNAMIC FEED COINJECTION PROCESS;
U.S. patent application Ser. No. 10/880,493 entitled COINJECTION MOLDING COOLED SHOOTING POT CYLINDER;
U.S. patent application Ser. No. 10/887,353 entitled APPARATUS AND METHOD FOR INJECTION MOLDING SHOOTING POT WEDGE FEATURE.
Thus, what is needed is a hot runner coinjection molding nozzle structure which allows melts with differing operating temperatures requirements to be processed through the same nozzle, allows close spacing of mold cavities, provides a removable tip with separate servicing of the different melt channels, provides a highly thermally conductive tip for efficient heat transfer, and is relatively inexpensive to design, install, and maintain.